Sulfur amino acid requirement of channel catfish: L-methionine and L-cystine.

Growth studies, utilizing a 24% crude protein diet containing an amino acid pattern similar to whole egg protein, indicate that the methionine requirement in the absence of cystine for fingerling channel catfish (Ictalurus punctalus) is about 0.56% of the diet (dry weight basis) or 2.34% of the dietary protein. The dietary requirement was confirmed by serum free methionine analysis. A marked increase in serum free methionine occurred at a dietary methionine level between 0.50% and 0.75% of the diet. The cystine replacement value for methionine on a mmole sulfur basis was found to be about 60%.